Macrocrystal ingot and method of making it



Patented Apr. 1, 1930 HANS; ALTEHTHUM, 0F BERLIN, GERMANY, ASSIGNOR TO GENERAL ELECTRIC COJHPANY, A CORPUHATION 015 NEW YORK V MAGROCRYSTAL INGOT AND TvTETI-IOD OF MAKING IT No Drawing. Application filed July 6, 1922, Serial No. 573,193, and in Germany July 13, 1921.

The metals consist of crystal grains, the size. of which is dependent on the thermic and mechanical pretreatment of the metals. The useful properties of these crystal grains are determined in a high degree by t ieir size and form. It is a disadvantage that in the course of time the size and form of these crystals vary, especially at high temperature. This phenomenon, known as recrystallization, takes place even in a very short time at high temperature and is extremely troublesome in many applications of the metals.

Metal pigs, bars, ingots, and similar shaped pieces according to the invention, are free from this troublesome phenomenon of recrystallization. They consist of only one or very few macroscopic crystals. This is recognized from the fact that on slight etching they show unitary reflecting surfaces and not, like the pieces of metal heretofore known, surfaces which reflect dilferently from spot to spot, and that, further, they split according to natural cleavage surfaces, and finally, on a somewhat ,deepetching even a round piece is etched angularly in aregular manner.

These bodies, remain unchanged in their properties and their structure if they are subjected to temperatures as high as desired for as long a time as desired, that is, they do not recrystallize, and they follow very simple laws in respect to their resistance to breakage and their extensibility, as well as their other mechanical properties. I Bodies may be made according to the invention if pressed metallic powder is kept for a considerable time at temperatures near the melting point of the metal in an environment such as a vacuum, indifferent or reducing gas atmosphere which is non-reactive with respect to the pressed powder. Thereby all the microscopically small crystals of the powder grow very gradually and almost uniformly until, aftera period of between some minutes and several hours, there is formed at some place a macroscopic crystal considerably larger than all the rest, which now absorbs its neighbors into itself in a compa.rafor example, a few minutes The crystal may continue to-grow so rapidly that finally the body consists of thisjsingle tively short time,

crystal. It may also happen that before the crystal is extended over the entire pressed body there are formed in a similar way at a few other points crystal germs, which then, each for itself, continues to grow until they collide with their previously formed neighbors of the same order of magnitude, with which however they do not combine. The body then consist of as many large crystals as there were germs which had formed during the time of its treatment and it is possible for example by mechanical division to make of the body several pieces, suitable for working each piece, consisting of a single macroscopic crystal. The time elapsing before crystallization occurs will be the shorter the higher the temperature chosen. As regards the number of crystals or what may be termed the macrocrystalline characteristic it is found that the number differs in ingots of equal size from different batches of the same metal made in the regular course of work, but in each individual batch the number is almost constant.

In metals, such as tungsten, which melt at high temperatures, it has been found that the process is to advantage carried on in a reducing atmosphere, and that then the macrocrystalline characteristic, that is, the number of crystals produced may be influenced by a certain small content of moisture in the gas.

' To this end it is preferable to conduct through sulphuric acid of a certain degree of concentration the hydrogen which surrounds the metal. For example, if the ingots of one batch of tungsten metal develop with hydrogen dried wtih extreme thoroughness from 8 to 10 crystals, then by passing the hydrogen through sulphuric acid, there will be only 3 to 5 crystals developed and if themoisture content is still further increased,- a single crystal will be obtained. Too great 21% increase of moisture leads to failure of the e ect.

Instead of giving to the hydrogen a pretube furnace by means of hydrogen at about 1000 to powdered tungstic metaL- This metal is divided into lots of 500 grams each which are pressed into bars in a compression press.

The pressed bars are heated for one half hour at 1300 in order to give them the necessary coherence for further treatment. A bar thus previously sintered is brought in a stream of very thoroughly dried hydrogen to a term "perature near the melting point by sending through it a low Voltage alternatingcurrent of high amperage and is kept at'this temperature for about one half hour and then is allowed to cool'oif. By etching, it is determined Whether crystallization has occurred, 'This' method of heating and testing by etching is repeated every half hour until th'e bo'dy is entirely transformed into macrocrystals. If

it consists of only one crystal the remaining E ingots of this batch of metal are heated with hydrogen of the same degree of dryness for the same period of time. If, on the contrary,

the ingot consists often macrocrystals, for

example, then in the next ingot the hydrogen is conducted through a Washing bot-tl e'with,

fifty per cent sulphuric acid, and isheated in the same way." Then if a bodyconsisting of one crystal is obtained the same method of operation is continued;otherwise the concentration of the sulphuric acid is varied until this end is attained. f

What I claim as new and desire to'secure by Letters Patent of the United States, is

1. The process of changing ainicrocrystah line'body of a refractory metal into .macrocrystal ingot having a substantially uniform macrocrystalline characteristic which con sist-s in heatin a body of pressedpowdered tungsten for a considerable timeat atemperature near the melting point of 'themetal'in an atmosphere ofa reducing gas which contains a' small percentage. of an oxidizing agent; 7

2. The process of changing a, pressed microcrystallihe body of arefractory metal into macrocrystal form the number of macrocrystals in equal 'units of lengthfofwhich is substantially'constant which'consists inheat ing the pressed microcrystalline body in areducing' gas a" considerabletinieto which an oxidizing component has been added, the per;

cent of which latter is varied as thenamber of macrocrystals' desired each unit length var es The process of changing a pressed "1111- crocrystalline body of a refractory metal into macrocrystal form which consists in heating the pressed microcrystalline body in a reducing gas not less than a substantial fraction of an hour to which an oxidizing agent adapted to be taken up by the gas has beenadded bypassing the gas through a material to which the agent has been previously added, the percentage of which agent taken upv by the gas is varied by varying the percentage of the agent in the material through which the gas passes.

4. The process of changing a pressed microciystalline body of a refractory metal into macrocrystal form which consists'in heating the pressed microcrystalline body in a reducing gas to which an oxidizingagent adapted to be taken'up by the gas has been added by" passing the gas through a material to which the agent has been previouslya'dded, the percentage of which agent taken upby the gas is varied by varying the percentage of the agent in the material through which the gas passes, which percentage is determined by the macrocrystalline characteristic desired in the body. j

'5. The process of ch 7 crocrystalline body of a refractory metal into macrocrystal form which consists in heating the pressed microcrystalline body in a reduc-- ing gas to which an oxidizing volatile agent adapted to' be taken up by the gas has been i anging'a'pressed mi 7 added by passing the gas through a non'- volatileliquid to which the agent hasbeen previously added, the percentage of which agent taken up by the gas is varied by varying the percentage of the agent in the material through which the gas is 'pas'sed','which per-. centage is determined bythe macrocrystal-- line characteristic desired in the body.

6. The process of changing a pressed microcrystalline body of the refractory metal into macrocrystal formwhich consists in heating the pressed-microcrystalline body in a reduoing'gas to which water vapor taken up by the gas has been added by passing the gas through sulphuric acid to which-Water has been previously added, the percentage of 1 which water vapor taken up by the 'gas'is varied by varying the percentage of the'water intheacid. P p 7. The process of converting a pressed ingot of refractory material into macrocrystalline form by heating in a hydrogen atmosphere with water vapor, which comprises 5 controlling the macrocrysta-llineformation of the refractory material: by regulating the amountof water vapor in said'a'tmosphere.

- 8. The process of converting a pressed in- 'got of refractorymaterial into macrocrys't'alline form by heating in a reducing atmosphere and containing'ja'n oxidizing gas, which comprises controlling the macrocrystalline'f formation of'the refractory material by regulating the amount of oxidizing jgasiinfsaid 

